In the 3rd generation partnership project radio access network long term evolution advanced (3GPP LTE-A), a method of connecting a channel for uplink user data information (hereinafter referred to as “uplink data”) and a channel for downlink user data information (hereinafter referred to as “downlink data”) to their respective optimum cells (independent uplink/downlink cell data transmission) is under consideration (see Non Patent Literature 1).
FIG. 1 shows a situation of independent uplink/downlink cell data transmission in which a physical downlink shared channel (PDSCH) is connected to cell #1 and a physical uplink shared channel (PUSCH) is connected to cell #2. A PDSCH is a downlink data channel in which downlink data is arranged and a PUSCH is an uplink data channel in which uplink data is arranged.
An independent base station apparatus (eNB, hereinafter referred as “base station”) is provided in each of cell #1 and cell #2, and backhaul between cell #1 and cell #2 is configured with an X2 interface. Here, when cell #1 is the cell having the best downlink channel quality for an LTE-A mobile station (hereinafter referred to as “mobile station”), and cell #2 is the cell having the best uplink channel quality for the LTE-A mobile station, in independent uplink/downlink cell data transmission, as shown in FIG. 1, a PDSCH is connected to cell #1, and a PUSCH is connected to cell #2.
Further, because a channel (for example, a PUCCH) for controlling feedback (FB) such as acknowledgement/negative acknowledgement (ACK/NACK) needs to transmit a feedback at a high speed, the FB control channel is connected to the same cell as for a downlink data channel, not the same cell as for an uplink data channel which provides an optimum link connection. If the FB control channel is connected to the same cell as for an uplink data channel which provides an optimum link connection, and communication between independent cells is performed via backhaul, such communication would take time on the order of several to several dozens of subframes, making it difficult to transmit feedback in the FB control channel at a high speed. However, when connecting to the same cell as for a downlink data channel, it is possible to transmit feedback in the FB control channel at a high speed.
As described above, in independent uplink/downlink cell data transmission, an uplink data channel and a downlink data channel are connected to their respective optimum cells. At this time, scheduling information (control information for designating modulation coding scheme (MCS) or resource block (RB)) needs to be reported to an LTE-A mobile station at a high speed.
In an LTE downlink channel, downlink scheduling information is reported using a PDCCH in the same subframe as the subframe containing the PDSCH in which downlink data is arranged. Further, in an LTE uplink channel, uplink scheduling information is reported to an LTE mobile station using a PDCCH four subframes before the subframe containing a PUSCH in which uplink data is arranged.
In an LTE-A, as a method of reporting uplink scheduling information, a method in which uplink scheduling information is transferred from cell #2 to cell #1 in real time and reported to an LTE-A mobile station using a PDCCH of cell #1, is possible. However, because it will take time to communicate via Backhaul in which cell #1 and cell #2 are connected with an X2 interface, it is difficult to transfer uplink scheduling information from cell #2 to cell #1 at high speed.
As another method, a method in which the base station of cell #2 transmits a PDCCH containing uplink scheduling information for an LTE-A mobile station to the LTE-A mobile station, is possible. For example, as shown in FIG. 2, downlink scheduling information for an LTE-A mobile station is transmitted using a PDCCH from the base station of cell #1 to which a PDSCH is connected, and uplink scheduling information for the LTE-A mobile station is transmitted using a PDCCH from the base station of cell #2 to which a PUSCH is connected. Here, if uplink scheduling information for an LTE mobile station is transmitted to the LTE mobile station in which the PUSCH is connected to cell #1 by containing the information in the PDCCH, as is conventionally done, the LTE mobile station in cell #1 can connect to cell #1, as is conventionally done, making it possible to maintain a backward compatibility with the LTE mobile station.